In the manufacture of semiconductor devices such as an integrated circuit (IC) and so forth, it is typical that a target object such as a semiconductor wafer or the like is repeatedly subjected to various kinds of processing such as film-forming, etching, heat-treating and reforming through the use of plasma or with no use of the same, thus producing a desired circuit device. For example, a single wafer processing apparatus is designed to perform heat treatments on a semiconductor wafer one by one. In this processing apparatus, a mounting table structure with a resistance heater and an electrostatic chuck is arranged inside a vacuum evacuable processing chamber. A semiconductor wafer is mounted on the upper surface of the mounting table structure. In this state, specific processing gases are fed to perform various kinds of heat treatments on the wafer under predetermined process conditions through the use of plasma or with no use of the same (see, e.g., Japanese Patent Laid-open Application Nos. 63(1988)-278322, 07(1995)-078766, 06(1994)-260430, 2004-356624, and 10(1998)-209255).
During the heat treatments, the semiconductor wafer is exposed to a high temperature and the processing chamber is supplied with a cleaning gas or corrosive gas such as an etching gas. In order to endure such a harsh environment, the mounting table structure for holding the semiconductor wafer tends to be made of ceramic represented by AlN (aluminum nitride). The heater and the electrostatic chuck are integrally molded from a ceramic material and buried in the mounting table structure.
Now, description will be made on one example of a conventional processing apparatus and a conventional mounting table structure. FIG. 14 is a schematic configuration diagram showing a conventionally available typical plasma processing apparatus. FIG. 15 is an enlarged cross sectional view showing a power-feeding portion of a mounting table structure. As shown in FIG. 14, a mounting table structure 4 for supporting a semiconductor wafer W on its upper surface is arranged within a cylindrical processing chamber 2. A shower head 6 as a gas introduction unit is provided in the ceiling portion of the processing chamber 2. In the lower surface of the shower head 6, there is formed a gas injection hole 6a through which to inject a necessary gas. A plasma-generating high-frequency power supply 8 of, e.g., 13.56 MHz, is connected to the shower head 6. The shower head 6 is designed to serve as an upper electrode.
The processing chamber 2 is provided with a gas exhaust port 10 formed in the bottom portion thereof so that the atmosphere within the processing chamber 2 can be evacuated through the exhaust port 10. The mounting table structure 4 includes a mounting table body 12 for holding the wafer W and a support column 14 upstanding from the bottom portion of the processing chamber 2 to support the mounting table body 12. The mounting table body 12 is made of a heat-resistant and corrosion-resistant material, e.g., ceramic such as AlN or the like. A lower electrode (not shown) to be supplied with high-frequency power and an electrode 16 serving as a chuck electrode of an electrostatic chuck are integrally buried in the mounting table body 12. A power-feeding rod 18 extends through the support column 14 and joins at its leading end to the electrode 16. If necessary, electric power is supplied from a power supply 20.
The joint structure between the electrode 16 and the upper end of the power-feeding rod 18 is shown in FIG. 15 which is an enlarged view of the area indicated by “A” in FIG. 14 (see, Japanese Patent Laid-open Application No. 10(1998)-209255). The electrode 16 within the mounting table body 12 is made of, e.g., Mo (molybdenum), W (tungsten) or an alloy thereof. A connection terminal 22 made of Mo or an alloy thereof is connected to the electrode 16 in advance. A recessed connection hole 24 is formed in the lower surface of the mounting table body 12. The connection terminal 22 is exposed into the connection hole 24 from the inner side of the latter. A power-feeding connector portion 26 provided at the tip end of the power-feeding rod 18 is inserted into the connection hole 24. A stress relaxing member 28 made of an alloy containing Co (cobalt) and/or Ni (nickel), e.g., Kovar (registered trademark) which is a Co—Fe—Ni alloy, is interposed between the power-feeding connector portion 26 and the Mo-containing connection terminal 22 in order to absorb the stress generated by the difference in thermal expansion. The connection terminal 22 and the stress relaxing member 28 are jointed to each other by, e.g., a Ni alloy brazing material 30. Likewise, the stress relaxing member 28 and the power-feeding connector portion 26 are jointed to each other by, e.g., a Ni alloy brazing material 32.
In the jointing process, the joint structure mentioned above is placed within a hot furnace in its entirety and baked at a high temperature. The power-feeding rod 18 and the power-feeding connector portion 26 are made of Ni (nickel) or its alloy. The leading end portion of the power-feeding rod 18 has a stepped portion and a reduced diameter portion, the latter of which serves as the power-feeding connector portion 26. A sleeve-shaped guide member 34 made of, e.g., Ni, is arranged on the outer circumferences of the power-feeding connector portion 26 and the stress relaxing member 28.
If the mounting table structure is repeatedly used at a high temperature of, e.g., 500° C. or more, the metals contained in the stress relaxing member 28, e.g., Fe, Ni and Co, are thermally diffused toward the connection terminal 22 and bonded to Mo. This creates a phenomenon that brittle intermetallic compounds are formed near the joint surfaces of the connection terminal 22 and the brazing material 30. Detachment occurs in the portion where the brittle intermetallic compounds exist, which poses a problem in that the power-feeding connector portion 26 is disconnected from the connection terminal 22.
This diffusion phenomenon is particularly remarkable in Co and Ni atoms. FIG. 16 is a diagrammatic image illustrating an electron micrograph of the area indicated by “B” in FIG. 15. It can be seen in FIG. 16 that the Co components present in the stress relaxing member 28 are thermally diffused into the brazing material 30 and further that a large quantity of Co elements 36 are accumulated in the interfacial surface area of the Mo-containing connection terminal 22 where it meets with the brazing material 30. Analysis reveals that the Ni components present in the stress relaxing member 28 and the brazing material 30 are also thermally diffused and accumulated in the boundary area of the connection terminal 22 where it meets with the brazing material 30. The phenomenon of becoming brittle would occur even if the material of the connection terminal 22 is changed from Mo to W (tungsten). There has existed a need to eliminate this phenomenon.